The US Department of Agriculture confirmed the detection of New World screwworm in a three-week-old calf in Zavala County, in South Texas, the first case of the flesh-eating parasite found in the United States since it resumed its northward spread from Central America in 2023. Larvae were identified in the animal's umbilical area, prompting an immediate emergency response.
The Animal and Plant Health Inspection Service said it had established a 12-mile 'infested zone' around the detection site, imposed quarantines and increased trapping for the pest along the border, while standing up an incident command team with the Texas Animal Health Commission. Targeted releases of sterile screwworm flies were being expedited to wipe out any breeding population in the area.
The New World screwworm is the larval stage of a fly that lays its eggs in the open wounds of warm-blooded animals; the maggots feed on living tissue, causing severe and potentially fatal damage to livestock, wildlife and, in rare cases, people. The parasite was eradicated from the United States decades ago through the sustained release of sterilised flies, a programme that prevents wild populations from reproducing.
Officials stressed that the food supply remained safe, noting that screwworms do not infest meat, fruit, vegetables or other food products. As of the announcement, there had been no further detections beyond the single calf, and authorities said the containment measures were intended to keep it that way.
The case nonetheless alarmed the cattle industry, for which a re-established screwworm population would pose a serious economic threat, raising the cost of monitoring herds and treating infestations. The parasite's gradual movement north through Central America and Mexico in recent years had put American officials on heightened alert.
State and federal agencies urged ranchers and pet owners to watch for wounds infested with maggots and to report suspected cases promptly, the kind of early detection that underpins eradication efforts. The response in Zavala County will test whether the sterile-fly strategy that cleared the pest before can again contain it at the border.